Fix TSC/BSIC handling bug and remove bts->tsc

This fixes a bug in the following circumstances:
* BSIC is set to 0 in the config file
* No TSC is explicitly specified at the BST level in the config file

In this case, we ended up using BSIC=0 and TSC=7, as TSC=7 is our
default initialization value.

The TSC of the CCCH/BCCH must always be the BCC, which is the lower 3
bits of the BSIC.  Having configuration options for both the BSIC _and_
the TSC at the BTS level therefore makes no sense, as it only adds ways
in which users can configure non-oprational configurations.  So we
remove the bts->tsc member, and keep only the ts->tsc members that allow
us to configure a timeslot-specific TSC that's different from the BTS
TSC (= BCC).
diff --git a/openbsc/src/utils/bs11_config.c b/openbsc/src/utils/bs11_config.c
index e8acb46..0d13e25 100644
--- a/openbsc/src/utils/bs11_config.c
+++ b/openbsc/src/utils/bs11_config.c
@@ -898,7 +898,7 @@
 		fprintf(stderr, "Unable to allocate gsm network\n");
 		exit(1);
 	}
-	g_bts = gsm_bts_alloc_register(gsmnet, GSM_BTS_TYPE_BS11, HARDCODED_TSC,
+	g_bts = gsm_bts_alloc_register(gsmnet, GSM_BTS_TYPE_BS11,
 					HARDCODED_BSIC);
 
 	/* Override existing OML callback handler to set our own. */